Piezoelectric actuators are typically employed in motion control systems that require very high resolution and controllable movements of objects. For example, these devices are often employed in optical measurement systems to perform very precise and controllable rotational movements of stages, mounts, and other components. NEW FOCUS™, which is part of Newport Corporation, manufactures and markets a piezoelectric actuator called PICOMOTOR™, often used in various optical applications. Hereinafter piezoelectric actuators will be referred to as PICOMOTOR™. In use, PICOMOTORS™ may achieve rotational movements as small as or smaller than 0.6 milliradian (mrad). Another benefit of PICOMOTORS™ is that they are able to retain their last position when they are powered off and subsequently turned on again.
Generally, PICOMOTORS™ and similar piezoelectric actuators are driven with relatively high voltage sources. For example, some piezoelectric actuators are driven with a drive voltage having peak value of around 120 Volts. The drive voltage actuates a piezoelectric material and causes the material to expand in a linear direction. A rotor or wheel is frictionally coupled to the piezoelectric material. For example, a PICOMOTOR™ uses the principle of dynamic and static friction in order to rotate the rotor or wheel in a specified direction. The drive voltage waveform, which usually takes the form of a defined pulse, is typically configured to rotate the rotor or wheel in the desired clockwise or counter-clockwise direction.
For example, if the drive voltage waveform has a relatively slow rising edge and a relatively fast falling edge, the rotor or wheel will rotate during the rising edge due to significant friction, and not substantially rotate during the falling edge due to slippage. Conversely, if the drive voltage waveform has a relatively fast rising edge and a relatively slow falling edge, the rotor or wheel will substantially not rotate during the rising edge due to slippage, and rotate during the falling edge.
Often, in such motion control systems, it would be desirable to determine whether a PICOMOTOR™ is connected to a drive voltage source or power driver. For many reasons, a PICOMOTOR™ may become disconnected from the power driver, such as by faulty wiring or disconnection of connectors. Because of the relatively high voltages involved in driving these types of piezoelectric actuators, faulty wiring and disconnected connectors may possess an inherent danger to users. Thus, it would be desirable for such motion control systems to alert a user and/or perform some other safety operation when a PICOMOTOR™ is not connected to the power driver.
Additionally, in such motion control systems, it would desirable to determine the type of PICOMOTOR™ connected to the power driver. Certain types of PICOMOTORS™ have certain limitations, and should be operated in a particular manner. For example, a first type or standard PICOMOTOR™ may be driven with a pulse rate that is much higher than the maximum pulse rate for a second type or tiny PICOMOTOR™. If the pulse rate applied to the second type or tiny PICOMOTOR™ significantly exceeds its maximum pulse rate, irreversible damage to the PICOMOTOR™ may occur.
Thus, there is a need to detect the presence and type of capacitive loads, such as piezoelectric actuators and PICOMOTORS™, which may be coupled to a power driver.